Gamma Spectrometry Measurements Research Articles

ITER materials irradiation within the D–T neutron environment at JET: post-irradiation radioactivity analysis following the DTE2 experimental campaign

Abstract This work presents the results following the first irradiation of ITER materials samples in a tokamak D--T plasma environment operating at significant fusion power. The materials exposed to this nuclear environment at the Joint European Torus during the DTE2 experimental campaign that took place in 2021 include representative ITER samples from various components such as poloidal field (PF) coil jacket samples, toroidal field coil radial closure plate steels, EUROFER 97 steel, W and CuCrZr materials from the divertor, Inconel-718, CuCrZr, and 316L stainless steel for blanket modules, as well as vacuum vessel forging samples.

The experimental results discussed include high-resolution gamma spectrometry measurements and analysis conducted with the post-irradiated samples, of which there were 68 in total. These samples were exposed through different experimental campaigns, including deuterium, deuterium--tritium and tritium phases. Supporting the analysis were 25 dosimetry foil-based neutron diagnostics and two 'VERDI' neutron spectrometry diagnostics. A further 12 samples for positron annihilation spectroscopy (PALS) were also irradiated. The irradiation of all these samples took place in a long-term irradiation assembly located near the JET vacuum vessel.

The post-irradiation analysis of the ITER material samples has yielded valuable insights into their material activation levels and radiation fields. Comparative assessments between experimental measurements and comprehensive neutronics simulations have demonstrated a significant level of agreement in this work, while also revealing some discrepancies in specific material instances. The data and interpretation from this work not only serve as a robust experimental foundation for enhancing the precision and predictability of neutronics simulation approaches for ITER and next-step devices but also present some opportunities for the refinement of simulation methodologies. In light of these findings, a series of recommendations have been proposed, aimed at improving confidence in nuclear predictions associated with materials that have been exposed to fusion nuclear environments and advancing understanding in this important domain.

Assessment of radiological hazards of soils from the city of Bitola (Macedonia) and its environs

ABSTRACT To establish the radioactivity level of soils and assess the associated radiological impact on residents, 58 samples from the town of Bitola and its environs were collected. After conducting gross alpha and gross beta measurements with a gas-flow proportional counter as a preliminary screening test, subsequent gamma-spectrometry measurements reveal the presence of 40K, 226Ra, 232Th, and 137Cs in the soil samples as radionuclides with the highest impact. The absorbed gamma dose rate, the annual effective dose, radium equivalent activity, external hazard index, gamma index, excess lifetime cancer risk, and annual gonadal dose were calculated using the obtained activity concentrations of the radionuclides. Upon comparison with similar studies conducted in the Balkan countries, the obtained results for radiation hazard indices were found to be the highest in the region. Coloured maps were generated to visually represent the spatial distribution of the absorbed gamma dose rate in air and annual effective dose, clearly indicating the combined influence of geology and human activities, including the nearby thermoelectric power plant operation.

Updating the alluvial mapping of the middle Loire catchment: Predictive geomorphology approach and mineralogical characterization of the deposits

This study aims to provide a full synthesis of recent work on the fluvial terraces of the middle section of the Loire River, between its exit from the “Massif Central” montane area and its entry into the Touraine region, with the aim of better understanding of the evolution of the river during the Pleistocene period.New fieldwork and topographic analyses (including a predictive geomorphology approach) permit updating the spatial extent and geometry of the different Quaternary alluvial sedimentary formations in this area. In addition, new analytical data were acquired both by X-ray diffraction (XRD) on heavy minerals and by gamma spectrometry measurements on alluvial sandy sediments. These analyses allow us to characterize and distinguish the alluvial formations.This work has identified three distinct periods in the history of the Loire: the oldest, corresponding to the deposition of sediments characterised by an abundance of metamorphic minerals, originating from the Massif Central; an intermediate period, corresponding to the deposition of the high terraces of the Loire system, not characterised by mineralogical analyses but by the approach of the predicted geomorphology showing different terrace geometries; lastly, a recent period comprising the low and medium altitude terraces, characterised by an abundance of volcanic minerals also originating from the Massif Central.

Radiological clearance of historical waste from particle accelerators

This paper presents a detailed methodology for reclassifying radioactive material from particle accelerators as non-radioactive, drawing on experiences at CERN. During particle accelerator decommissioning, the waste is classified based on its radioactivity level where the very-low-level activity material is the potential clearance candidate. Complying with the Swiss legislation, the waste must fulfil three criteria in order to be cleared. Before performing the radiological measurements, the waste must be processed (disassembled, cut, … ) due to its size and multi-material composition. To properly evaluate the measurement results, a detailed theoretical study must be performed providing information on e.g. expected radionuclides. As a part of quality assurance, the theoretical models are verified using gamma spectrometry measurements on waste samples. The presented methodology is supported by the summary of past and ongoing CERN projects as well as know-how learned by years of experience.

Application of machine learning methods for spent fuel characterization based on gamma spectrometry measurements

Machine learning models have been developed to predict properties of spent nuclear fuel assemblies from Paks NPP, such as burnup, cooling time, initial enrichment, and Pu-239 content. Measured gamma spectra are processed, and activity ratios of fission products are calculated to serve as input features for Support Vector Regression, Random Forest, and Multi-Layer Perceptron models. Data uncertainty is considered during inference to produce prediction intervals, and input features are ranked using the Gini importance of Random Forest models. A deep learning approach using Convolutional Neural Networks has also been developed to predict the spent fuel parameters from the measured spectra directly. The new models can predict spent fuel parameters with great precision, outperforming earlier approaches that rely on nonlinear regression using a single feature to predict burnup and cooling time and can estimate initial enrichment and Pu-239 content.

Evaluation and reduction of background interference caused by airborne particles in gamma spectrometry measurements

Gamma-ray spectrometry has wide applications in various fields of science, technology, medicine, and basic research. Despite many advantages of this technique, background quantification constitutes one of the challenges in performing measurements. This study aimed to show the effect of air pollution on gamma spectrometric measurements and provide a low-cost system to improve their quality. To improve the background parameters of the spectrometer, a special system was implemented to ventilate the detector chamber, where the air stream is cleaned using a HEPA (High Efficiency Particulate Air) filter and nitrogen evaporating from the dewar's vessel.. A strong correlation was observed between the concentrations of particulates in the air and the level of count rates in specific areas of the gamma spectrum. For example, the results show a significant effect of reductions in the average number of counts within the 46.5 keV line of the 210Pb isotope, where the background decreased by 71 %.

Modeling gamma detectors in OpenMC: Validation of a newly implemented pulse-height tally

Gamma spectroscopy measurements can be simulated using a pulse-height tally functionality of Monte Carlo particle transport codes. Such a functionality must account for the complete simulation history of a particle’s energy deposited in a particular volume. OpenMC, an open-source application for neutron and photon particle transport which is widely used in the nuclear engineering community, previously lacked adequate simulation capabilities for gamma spectroscopy. In this paper, we outline the implementation of the photon pulse-height tally for OpenMC. Additionally, we validate the new function by comparing results to analytical calculations, other software, and experimental data.

Gamma-spectrometry measurements of filtration media from an Advanced Gas-cooled Reactor

Filtration media used to quantify particulate and gaseous releases have been collected from Hartlepool Power Station in the United Kingdom and measured using high-sensitivity gamma-spectrometry systems. Radionuclides that are relevant to the monitoring regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) have been detected. Results are reported and compared to detections recorded on the International Monitoring System (IMS). Time series activity plots have been produced and results interpreted with respect to known plant activities. The reported results improve the understanding of trace-level radionuclide emissions from Advanced Gas-cooled Reactors (AGRs) and aid interpretation of IMS measurements. This work is being performed as part of the Xenon Environmental Nuclide Analysis at Hartlepool (XENAH) collaboration between the Atomic Weapons Establishment (AWE, UK), EDF Energy (UK), Pacific Northwest National Laboratory (PNNL, US) and the Swedish Defence Agency (FOI, Sweden).

Gamma-emitting radionuclides in therapeutic muds of the Euganean Thermal District (Padua, Italy)

Mud therapy is a therapeutic tool which uses natural materials available in the environment for healing purposes (clays and thermal water). The use of natural remedies increases the compliance to the cure, and their success is increasing in the last decades, all over the world. As natural matters, also muds have a wide range of composition, so, their use for healing requires appropriate knowledge.One of the most important world reference area for mud therapy has been accessed for sampling in different thermal centers (28) and also the exploiting site of raw clay has been studied. High resolution gamma spectrometry measurements have been acquired, compared with previous published data and discussed considering other compositional parameters.A clear increase of radionuclides of the 238U series characterize therapeutic muds respect to raw materials, 226Ra in particular. The scavenging of Ra from thermal waters is considered to occur after the precipitation of sulfate minerals (gypsum, barite) into the mud matrix, and several lines of evidence suggest that the repeated contact with thermal water (mud recycling) enhance the enrichment of Ra. A different scenario can be drawn for workers and for patients, as their contact with the mud is different for type and time. The dose arising from working in the area of therapeutic muds preparation and the dose to the skin of patients have been calculated.Even if Euganean therapeutic muds are richer in 226Ra respect to other similar materials, no radiological hazards emerged for workers who manage the preparation area, even in the most cautionary scenario. Also for patients, the contribution of Euganean mud therapy to the annual equivalent dose to skin is negligible, according to the cautionary elaboration done. Also considering literature data on the transcutaneous passage of chemical elements with geochemical affinity with Ra, no radiological hazard is detectable.

Charge transport comparison of FA, MA and Cs lead halide perovskite single crystals for radiation detection

We report a systematic comparison of the charge transport and radiation detection properties of inorganic and organic metal bromide single crystal perovskites. We studied the performance of Bridgman-grown CsPbBr3 single crystals, together with solution-grown FAPbBr3 and MAPbBr3 single crystals. Laser time of flight is used to measure the drift mobilities for all samples, and we report a maxium mobility value of 121 ± 10 cm V−1 s−1 for CsPbBr3. Alpha particle measurements were used to assess the mobility-lifetime products, with values recorded in the range of 2 × 10−4 cm2 V−1 to 1 × 10−3 cm2 V−1. Low temperature measurements showed an increase in bulk resistivity at temperatures down to 260 K, but no significant change to the drift mobilities. The overall performance of the Cs, FA and MA samples is compared and their potential for use in gamma spectroscopy measurements is discussed.

Spent Nuclear Fuel passive gamma analysis and reproducibility: Application to SKB-50 assemblies

This work studies the reproducibility of passive gamma spectroscopy measurements for spent nuclear fuels (SNFs). The fifty assemblies used for this study span over a variety of initial enrichments, burnups, and cooling times. These SNFs have been measured in two different gamma axial measurement campaigns. The net peak counts are determined for Cs-137, Eu-154 and Cs-134. Furthermore, a sensitivity analysis of the relative position of the SNF and the detector is performed. Most importantly, this work describes a methodology using an intrinsic self-calibration procedure that can be used to compare the relative activities of the radionuclides without the need for detailed knowledge about the measurement set-up and its properties. The reproducibility of the Cs-137 net peak count rate ranges between 2% and 4%. Systematic reproducibility of the ratio of Eu-154 and Cs-134 to Cs-137 is between 0,4% - 5 % using the intrinsic self-calibration method.

Optimisation of gamma spectrometry measurements in atmosphere during nuclear emergencies.

During emergencies following a major nuclear accident a prompt and accurate characterisation of the radioactive cloud is one of the main task of any radioactivity monitoring system. This task is usually performed by means of γ-spectrometry High Purity Germanium (HPGe) measurements on atmospheric particulate samples gathered by means of high-volume pumps. The key parameters describing the performances of a monitoring system are the Minimum Detectable Activities (MDAs) of the most relevant radionuclides. These parameters depend on a number of factors related to the efficiency of the available germanium detector, the volume of air filtered by the sampling devices and the γ-decay scheme of each radionuclides as well. Besides the MDAs, another very important characteristic of a monitoring system, especially during an evolving emergency, is its capability of giving reliable results at a given and constant pace. It is therefore important to define the time resolution of the monitoring system, i.e. the minimum time needed to produce the data, namely the activity concentrations of the radionuclides in the atmosphere. The optimization of the measurements procedures are discussed in this work: in particular it is demonstrated that, being t the time resolution of the monitoring system, the lowest MDAs can be achieved with a sampling time given by (2/3)·t and a counting time of (1/3)·t. Finally, the MDAs achievable for a standard monitoring system based on a 30% HPGe detector are calculated for all the most important fission products.

Study of the matrix composition effect on gamma spectrometry analysis using Monte Carlo simulation: application for soil to crop transfer factor determination

Abstract Self-absorption effect has a significant impact on gamma spectrometry measurement for the highly precise determination of the radionuclides activity. Among the main factors affecting the self-absorption effect especially at low gamma energies is the matrix composition of the sample. For this purpose, we studied the matrix composition effect on the self-absorption correction for plant and soil matrices using a Monte Carlo simulation model, composed of High Purity Germanium (HPGe) detector and a cylindrical geometry source. The simulated configuration model was validated by comparison of simulated full energy peak efficiency (FEPE) values with the experimental ones using a standard radioactive solution, covering large interval gamma energies in the range of 59.54–1836.12 keV. The results show that the FEPE values of low gamma energies are affected by the matrix composition, where in the soil matrix the FEPEs decreased by 36% and only by 1% in the plant matrix. The Monte Carlo results were applied in order to accurately calculate the transfer factor of the environmental radionuclides 226Ra, 232Th and 40K from soils to several crops, mustard, artichoke and fennel through their specific activities.

Distribution of Natural Radionuclides and 137Cs in Urban Soil Samples from the City of Novi Sad, Serbia-Radiological Risk Assessment.

This work presents the natural radioactivity distribution of 21 surface soil samples taken in the city of Novi Sad, Serbia. The analysis for radioactivity was performed using a gas low-level proportional counter for gross alpha and gross beta activity, while the specific activities of radionuclides were determined using HPGe detectors. The gross alpha activity of 20 samples was below the minimum detectable concentration (MDC), while in 1 sample it was 243 Bq kg-1; the gross beta activity ranged from the MDC (11 samples) to 566 Bq kg-1. The gamma spectrometry measurements showed naturally occurring radionuclides 226Ra, 232Th, 40K, and 238U in all investigated samples, with average values (Bq kg-1) of 33.9, 36.7, 513.8, and 34.7, respectively. Natural radionuclide 235U was detected in 18 samples with activity concentrations in the range of 1.3-4.1 Bq kg-1, while in the other 3 samples, the values were below the MDC. The artificial 137Cs radionuclide was detected in 90 percent of the samples, with a maximum value of 21 Bq kg-1, while the other artificial radionuclides were not detected. Based on the obtained concentrations of natural radionuclides, hazard indexes were estimated, and radiological health risk was assessed. The results present the absorbed gamma dose rate in the air, annual effective dose, radium equivalent activity, external hazard index, and lifetime cancer risk.

The Second EWGRD Round Robin: Inter-Comparison of93mNb Measurements

Following on from an initial Round Robin inter-comparison of gamma spectrometry measurements reported in 2014, this paper presents the results of the second part of a further Round Robin inter-comparison commissioned in 2018 by the European Working Group on Reactor Dosimetry. The purpose of the exercise was to demonstrate the level of consistency between different organisations’ measurements of the93Nb(n,n’)93mNb reaction, which plays a key role in underwriting reactor dosimetry assessments. To achieve this, measurements of93mNb activity were performed by twelve European organisations on six sets of near identical niobium samples, each having its own geometry and tantalum concentration. The samples were provided by CEA, France and irradiated in the MARIA reactor, operated by National Centre for Nuclear Research, Poland. Participants provided their results to an independent referee who collated and compared the data. The inter-comparison has demonstrated agreement to within standard deviations ranging from ±2.2% to ±7.9%, with a tendency for some organisations to measure elevated values. The results of the inter-comparison are presented in an anonymised form together with discussion and conclusions which may be drawn from the exercise.

The Second EWGRD Round Robin: Inter Comparison of Gamma Spectrometry Measurements on Activation Dosimeters

Following an initial Round Robin inter-comparison of gamma spectrometry measurements reported in 2014, this paper presents results from the first part of a second Round Robin inter-comparison commissioned by the European Working Group on Reactor Dosimetry in 2018. Measurements were performed by thirteen European organisations on a set of irradiated neutron activation detectors representative of those commonly used by the Reactor Dosimetry community to measure neutron fluence using gamma spectrometry methods. The radionuclides measured were110mAg,58Co,60Co,54Mn, and46Sc. The purpose of the exercise was to demonstrate the level of consistency between participating organisations in blind tests of measurements. The samples used were disks of iron, nickel, titanium, and two standard alloys of aluminium, one of 1% cobalt and the other 1% silver. They were irradiated in the MARIA reactor operated by National Centre for Nuclear Research, Poland. Participants provided their results to an independent referee who collated and compared the data. The results are presented in an anonymised form together with discussion and conclusions which may be drawn from the exercise. Good agreement was obtained with standard deviations for individual measurements between 2.0% (54Mn) and 5.6% (60Co). Overall, the results obtained from the latter Round Robin show less consistency than those from the first Round Robin, which is attributed to the participation of a wider pool of organisations.

Radioactivity Content and Dosimetric Assessment in Bovine Meat from the Calabria Region, Southern Italy

In this article, the assessment of the radioactivity content in bovine meat from the Calabria region, Southern Italy, was performed. For this purpose, High Purity Germanium (HPGe) gamma spectrometry measurements were carried out in order to investigate any possible radioactive contamination by natural (40K) and anthropogenic (137Cs) radionuclides. Experimental mean values were found to be in the range from (78.9 ± 10.5) Bq kg−1 to (88.2 ± 12.5) Bq kg−1 for 40K and lower than the minimum detectable activity (MDA) in all cases for 137Cs, respectively. Moreover, any possible radiological health risk was also estimated, by calculating the total annual effective dose due to the ingestion of bovine meat by adult members of the population and by comparing it with the total natural radioactivity value (external + internal) for humans. Obtained values are in the range from 10.3 µSv y−1 to 11.5 µSv y−1, several orders of magnitude lower than the value of the total exposure to natural radioactivity for human beings, i.e., 2.4 mSv y−1. It is worth noting that the used approach could be used, in principle, for the evaluation of the radiological risk due to the presence of radionuclides in a large variety of food samples of particular interest, and thus it can constitute a guideline for investigations focused on the monitoring of food quality.

2D inversion of in situ gamma-ray spectrometric measurements of 137Cs for site characterization

Environmental contamination by radioactive materials can be characterized by in situ gamma surface measurements. During such measurements, the field of view of a gamma detector can be tens of meters wide, resulting in a count rate that integrates the signal over a large measurement support volume/area. The contribution of a specific point to the signal depends on various parameters, such as the height of the detector above the ground surface, the gamma energy and the detector properties, etc. To improve the spatial resolution of the activity concentration, contributions of a radionuclide from nearby areas to the count rate of a single measurement should be disentangled. The experiments described in this paper, deployed 2D inversion of in situ gamma spectrometric measurements using a non-negative least squares-based Tikhonov regularization method. Data were acquired using a portable LaBr3 gamma detector. The detector response as a function of the distance of the radioactive source, required for the inversion process, was simulated using the Monte Carlo N-Particle (MCNP) transport code. The uncertainty on activity concentration was calculated using the Monte Carlo error propagation method. The 2D inversion methodology was first satisfactorily assessed for 133Ba and 137Cs source activity distributions using reference pads. Secondly, this method was applied on a 137Cs contaminated site, making use of above-ground in-situ gamma spectrometry measurements, conducted on a regular grid. The inversion process results were compared with the results from in-situ borehole measurements and laboratory analyses of soil samples. The calculated 137Cs activity concentration levels were compared against the activity concentration value for exemption or clearance of materials which can be applied by default to any amount and any type of solid material. Using the 2D inversion and the Monte Carlo error propagation method, a high spatial resolution classification of the site, in terms of exceeding the exemption limit, could be made. The 137Cs activity concentrations obtained using the inversion process agreed well with the results from the in-situ borehole measurements and those from the soil samples, showing that the 2D inversion is a convenient approach to deconvolute the contribution of radioactive sources from nearby areas within a detector's field of view, and increases the resolution of spatial contamination mapping.

A Technique for Metallic Waste Characterization and Segregation in Management Routes

Adequate radiological characterization is important for optimization of metallic waste management. For decommissioning planning, the objective is to obtain a radiological understanding of the involved installation. The characterization at this stage could be carried out by means of: 1) neutron activation calculations based on reactor design and neutron flux; 2) dose rate measurements; 3) in-situ gamma spectrometry; 4) sampling for determination of the scaling factors in activated and contaminated components. During dismantling, in-situ characterization is carried out to classify and package the generated waste. Then, the packages are monitored for assessment of activity and determination of the management route. The selection of cutting and decontamination techniques should be based on accurate determination of the radionuclides inside the material and/ or on the surface contamination. . It is important to decide in which cases the decontamination will be efficient as well as to select the appropriate decontamination techniques based on whether the waste is slightly activated or contaminated or both. Α Semi-empirical technique for optimization of determination of contamination and activation of components and metallic waste is under development based on combination of gamma spectrometry measurements and MCNPX Monte Carlo simulations. Firstly, the technique aims at reduction of the uncertainties related to the density and activity distribution. The specific activities inside and on the surface of the materials could be determined by using the measurement results of the proposed non-destructive technique in combination with the use of the scaling factors for activation and/ or contamination.

Factors controlling 137Cs distribution in bottom sediments of Koronowo Reservoir (Poland)

PurposeThe main aim of this study was to investigate factors influencing the long-term distribution of 137Cs activity concentrations in the bottom sediments of the dam lake, Koronowo Reservoir, 32 years after the Chernobyl nuclear power plant accident. For this purpose, selected properties of the collected sediment samples, such as grain size, mineralogical composition, and organic matter (OM) content, were investigated.Materials and methodsThe samples of lake sediments were collected with a Kayak-type gravity corer. The spatial and vertical distributions of 137Cs and 40K activity concentrations in the bottom sediments were investigated based on gamma spectrometry measurements. The particle size distribution of surface lake sediments was determined using a laser particle size analyzer. SEM and XRD were used for the mineralogical analysis of the collected sediment samples. Additionally, the content of organic matter was examined in all samples using an elemental analyzer.ResultsThe 137Cs content was significantly elevated in the case of fine-grained (< 63 µm) surface lake sediments (classified as silts, which are deposited in the profundal zone of Koronowo Lake) and ranged from 12.5 ± 4.1 to 29.2 ± 4.0 Bq kg−1. It was found that the increased concentration of 137Cs activity is more closely related to the content of the silt fraction (2–63 µm) than to the clay fraction (< 2 µm) in the collected surface lake sediments. The content of clay minerals also showed a significant positive correlation with 137Cs activity concentration in the surface lake sediments of Koronowo Lake. A similar relationship was noticed for the OM content, but it may be suspected that it is the result of radiocesium-bearing particle accumulation in OM-rich sediments.ConclusionThe most important factor influencing the spatial distribution of 137Cs activity concentrations in the surface lake sediments of Koronowo Lake, apart from the bottom morphology and grain size of sediments, is the content of clay minerals. Moreover, the increased detrital inflow to the lake after the construction of the dam could have probably affected the vertical distribution of 137Cs activity concentrations in the bottom sediments, as evidenced by, e.g., the measurements of 40K activity concentration.